Electrode system for cathode ray tubes



Aug. 7, 1956 B. HENSEL ELECTRODE SYSTEM FOR CATHODE RAY TUBES Filed NOV. 27, 1953 iinited States Patent i ELECTRODE SYSTEM FOR CATHODE RAY TUBES Bernhard Hensel, Berlin-Friedenau, Loewe Opta Aktiengesellschaft, many, a company of Germany Germany, assignor to Berlin-Steglitz, Ger- At electron beam tubes of common construction the electron-emitting cathode is arranged coaxially with the axis of the electron beam, the electron-emitting spot being located on the end-wall of the cathode .cylinder which in its interior houses the hairpin-shaped heater filament. The control electrode (Wehnelt cylinder) of such systems is designed as a cylinder coaxial with the cathode; this cylinder is closed, at the end next to the beam, by a wall through the central aperture of which the electrons are passing into the discharge space.

This commonly used system has the fundamental disadvantages that, firstly, the arrangement of the cathode unnecessarily enlarges the length of the system in the direction of the tube axis and that, secondly, the very small distance between the electron-emitting spot and the Wehnelt cylinder cannot be kept constant owing to the inevitable small changes of the length of the cathode due to the heating of the latter.

These disadvantages are avoided by the present invention. The subject of this invention is a novel electrode system for electron beam tubes, the characteristic features of which are the following ones: The cathode designed as a narrow cylinder is not arranged .coaxially with the axis of the tube but perpendicularly to it and, in connection with this arrangement, the electron-emitting spot is not provided on the end-wall of this cathode cylinder but on its cylindrical surface. Thus, the heating filament arranged inside the cathode cylinder .can be designed in such a manner that a particularly concentrated heat emission will be achieved at that place which corresponds to the electron-emitting spot mounted on the outside surface of the cylinder. This can be accomplished e. g. by providing the helix of the heating filament at this place with a smaller pitch than otherwise or by choosing the diameter of the heating filament at this place of particularly concentrated heat emission smaller than along the rest of its length.

The control electrode (Wehnelt cylinder) at the cathode described before is designed, according to the present invention, in such a manner that it consists of either one or two discs arranged parallelly to the cathode axis or that the axis of the control electrode is likewise arranged perpendicularly to the direction of the electron beam, i. e. that the control electrode is coaxial with the heating cylinder. In this case the aperture for .the passage of the electrons is not provided, as usually, in the end-face wall of the Wehnelt cylinder but in the cylindrical surface of the control electrode.

Another advantageous embodiment of the electrode systern corresponding to the present invention consists in providing several individual electron-emitting spots on the cylindrical cathode body along its axis, each of these emission spots being surrounded by a corresponding control cylinder. Such a design is recommendable mainly for multi-beam tubes with individual independent control of the electron beams. l

The invention will be described in connection with the drawings referring to three diiierent examples:

In Fig. l an electrode system is shown which is designed 2,758,234 Patented Aug. 7, 1956 as a at barrel, in Fig. '2 an arrangement in which the cathode and the Wehnelt cylinder are mounted coaxially, in Fig. 3 a multi-beam system basing 'on the principle of Fig. 2, in Figs. 4 and 5 further improvements are shown.

All these drawings are considerably enlarged compared with real size; at Fig. 3, however, the enlarging factor is smaller than at the other drawings. In all these drawings only those parts are shown which are necessary for understanding the invention.

In Fig. 1 the tubular cathode 1 made of insulating material and housing the heating filament 2 is shown in cross section. The heating filament 2 is helically found about in the center of the cathode body 1 `respectively the pitch of the filament helix is smaller at this .place than along the rest of its length. On the outside, i. e. on the cylindrical surface of the cathode body 1, an oxide spot 4 is provided at the place corresponding to spot 3 at which the heating filament 2 has its greatest heat emission. The electrons emitted at heating from the emission spot 4 result in the electron beam, passing, as marked by the dotted lines, about perpendicularly to the axis of the cathode into the discharge space. The cathode 1 is mounted inside a ring or a cylinder 5, the axis of which is arranged perpendicularly to that of the cathode. The space enclosed by the ring 5 is closed, like a barrel, by two metallic discs 6 and 7. That part of disc6 which is next to the emission spot 4 is provided with a small aperture 8 through which the electron beam passes. The length of the cathode body 1 is chosen so that-see the left end of this cathode 1 in the drawing-a .certain clearance is provided inside cylinder 5 in order to avoid distortions or other mechanical damages of cathode 1 caused by the extension resulting from the heating of the cathode.

In the arrangement according to Fig. 1 Ieither plate 6 can be designed as a control electrode to which the corresponding control voltage is fed. ln this case it is recommendable to bring plate 7 to the potential of the cathode. Eventually, plate 7 .could be in this case made of some non-metallic material or even lbe omitted. Another design consists in employing plate 7, too, as a control electrode, in providing oppositely to it an oxide spot on the outside wall of cathode 1, and in providing plate 7, just as plate 6, with va central aperture. Such an arrangement can be employed e. g. for a special tube with two oppositely arranged picture screens between which the cathode and the control electrode respectively the control electrodes are mounted in the middle.

The ring-shaped cylinder 5 shown in Fig. l can be simultaneously employed as the base for the whole construction of the system, e. g. by mounting the rst anode of the electrode system on that rim of cylinder 5 which is located upmost in the drawing.

According to Fig. 2, showing a partially opened sideview, the cathode consisting, just as in Fig. l, of the elements 1, 2, 3, and 4 is concentrically embraced by a cylindrical control electrode 9. rIhis control cylinder 9 is provided with a small aperture 10 for lthe passage of the electrons whereat the radial direction of the aperture 10 corresponds to the position of the emission spot 4 on cathode 1. In case of need, at this arrangement, too, the cathode 1 can be provided with several emission spots distributed around the circumference of its cylinder, whereat each emission spot corresponds to one `aperture in the surface of control cylinder 9.

At the multi-beam system .according to Fig. 3 the cathode cylinder 1 is provided with several emission spots 11, 12, `and 13 arranged in axial direction which are embraced by corresponding control cylinders 14, 15, and 16 with the exit apertures 17, 18, and 19. In Iall three designs shown in the drawing the bifil'ar heating filament 2 is hairpinshaped 'and mounted inside the cathode cylinder. The new construction however renders also possible, in case of need, a straight-shaped heating filament, its connections projecting from both end-Walls of the cathode cylinder.

An improvement of the invention consists in arranging the emission spot not directly on the outside surface of the cylinder embracing the heating filament but on a conical or calotte-shaped boss projecting from the outside surface of the cathode cylinder by a small height of about l to 2 mm. This boss can be shaped either by a corresponding construction of the cathode cylinder itself, e. g. by pressing or drawing outwards that part which shall be provided with the emission spot whereby a prominence of preferably circular circumference with a diameter of 2 to mm. 'and a height of 1 to 2 nun. results. Instead the boss can also be designed as an individual member which is fixed, by welding or riveting, on the outside surface of the cathode cylinder whereat this cathode cylinder is previously provided with a preferably circular opening through which the heat of the heating filament can well come into contact with the surface supporting the cinissive material.

The novel design of the cathode has in particular the advantage that the capacity between the emission spot and the closely adjacent Wehnelt electrode will be diminished and that, furthermore, it will be 'avoided that the Wehnelt electrode is heated by too immediate neighborhood of the cathode body.

Fig. 4 represents the invention applied to such a cathode yat which the calotte-shaped boss is designed as an individual member arranged above an aperture in the cathode cylinder.

Fig. 5 shows the invention as applied to such a cathode in which the bosses for the emission spots are shaped by simply pressing, drawing or creasing outwards the tubular wall of the cathode. Besides th-at, Fig. 5 shows the application of the principle of the invention to 'a multi-beam tube.

ln both drawings are shown only the cathode and the Wehnclt electrode.

In Fig. 4 the cylindrical cathode is designated with 1; inside of it the preferably bilar heating filament 2 is arranged which has its greatest heat emission about in its center part. Above this center part is provided, according to the invention, a calotte-shaped boss 3 covering a circular opening 4 the diameter of which is 'about from 2 to 5 mm. On the surface of the boss 3 the emission layer 5 is deposited. Oppositely to it an electrode type Wehnelt 7 is arranged in the usual small distance with a central opening 6 vis-a-vis of it. In distinction from the usual design this Wehnelt electrode is built as a simple circular disc xed to a ceramic ring 8. The cylindrical cathode 1 is arranged diametrically to this ceramic ring 8. This `arrangement of cathode 1 diametrical to the holding ring renders recommendable the design of a cathode with c. g. square or rectangular cross section whereby a better conta-et of the cathode with the rim edge of the holding ring y8 is warranted. Instead of that, the rim edge of the holding ring 8 can be provided e. g. with a semicircular indentation for supporting the cathode 1 if -a cathode with cylindrical cross section is employed.

The design of Fig. 5 is different from that of Fig. 4 mainly in the following items: The emission spots on the surface of the cathode are not applied to individual caps as in Fig. 4 but the cathode wall is provided at these spots with corresponding bosses which are made by pressing, drawing, or creasing. Besides that, this example shows three bosses 9, 10, and 11 which are evenly distributed on the wall surface of the cathode in axial direction and which are covered with the corresponding emission spots i2, 13, and 14. This multiple arrangement of emission spots is provided for multi-beam tubes which are employed c. g. for colour television. Another difference of the design according to Fig. 5 from that of Fig. 4 consists in that the electrode type Wehnelt is not designed `as `a flat disc, but as cylinders 15, 16, and 17 concentric with cathode l in which passage apertures 1S, 19, and 20 are provided at the places opposite to the emission spots 12, 13, and 14. Between the individual Wehnelt cylinders insulating rings 21 respectively 22 are mounted in order to be able to feed, e. g. for colour television, each of these cylinders with its own control voltage independent from that of the two others. The two concentric electrodes: the cathode 1 on one side and the set of Wehnelt electrodes 15, 16, xand 17 on the other are suitably connected by two discs 23 respectively 24 of ceramic material; these discs 23 and 24 are the end walls of this concentric arrangement of electrodes and, for this purpose, are provided with corresponding grooves for inserting the two cylinders 1 and 15 respectively 17.

At the designs shown in the drawings it is not necessary to provide a special insulating l-ayer between the heating filament 2 yand the metal-made wall of cathode 1 because the normally used heating filaments have a fused and therefore insulating surface. Care must be taken, however, for mounting the heating filament inside the cathode tube free from 'any vibrations what can be accomplished by known means.

What l' claim is:

l. In an electron beam tube of the fluorescent screen type an indirectly heated cylinder-shaped cathode, the axis of which is arranged perpendicularly to the tube axis, and an electron-emitting spot carried by the cylindrical surface of said cathode.

2. In an electron beam tube of the fluorescent screen type an indirectly heated cylinder-shaped cathode, the axis of which is arranged perpendicularly to the tube axis, and an electron-emitting spot carried by the cylindrical surface of said cathode, said cathode being connected by isolating means with a plate-shaped control electrode.

3. In an electron beam tube of the fluorescent screen type an indirectly heated cylinder-shaped cathode, the axis of which is arranged perpendicularly to the tube axis, and an electron-emitting spot carried by the cylindrical surface of said cathode, said cathode being diametrically arranged inside an isolating ring, the end faces of which carry plates serving as control electrodes.

4. In an electron beam tube of the fluorescent screen type an indirectly heated cylinder-shaped cathode, the axis of which is arranged perpendicularly to the tube axis, and an electron-emitting spot carried by the cylindrical surface of said cathode, said cathode being surrounded by a concentric cylindrical control electrode connected with the cathode by isolating rings.

5. in an electron beam tube of the fluorescent Screen type an indirectly heated cylinder-shaped cathode, the axis of which is arranged perpendicularly to the tube axis, and the cylindrical surface of which is provided with several electron-emitting spots arranged along its axis.

6. In an electron beam tube of the fluorescent screen type an indirectly heated cylinder-shaped cathode, the axis of which is arranged perpendicularly to the tube axis, and the cylindrical surface of which is provided with several electron-emitting spots arranged along its axis, said cathode being surrounded by several separate con- 'centric cylindrical control electrodes arranged along its axis.

7. In an electron beam tube of the fluorescent screen type an indirectly heated cylinder-shaped cathode, the axis of which is arranged perpendicularly to the tube axis, and the cylindrical surface of which is provided with several electron-emitting spots arranged along its axis, said cathode being surrounded by several separate concentric cylindrical control electrodes arranged along its axis, and connected with one another and with said cathode by isolating means.

8. In an electron beam tube of the fluorescent screen type an indirectly heated cylinder-shaped cathode, the axis of which is arranged perpendicularly to the tube axis, and the cylindrical surface of which is provided with several electron-emitting spots arranged along its axis, said cathode being surrounded by several separate concentric cylindrical control electrodes arranged along its axis, said control electrodes being provided with apertures arranged in the direction of the electron beam radially emitted from said spots.

9. In an electron beam tube of the uorescent screen type an indirectly heated cylinder-shaped cathode, the axis of which is arranged perpendicularly to the tube axis, and an electron-emitting spot carried by the cylindrical surface of said cathode, the heating lilament mounted within said cathode being shaped in such a manner that an enlarged heat emission is effected behind the electronemitting spot.

l0. In an electron beam tube of the fluorescent screen type an indirectly heated cylinder-shaped cathode, the axis of which is arranged perpendicularly to the tube axis, and a calotte-shaped boss carried by the cylindrical surface of said cathode, and an electron-emitting material carried by said boss.

11. In an electron beam tube of the iiuorescent screen type an indirectly heated axis of which is arranged perpendicularly to the tube axis,

cylinder-shaped cathode, the 20 and a calotte-shaped boss carried by the cylindrical surface of said cathode which is provided with an aperture closed by said boss, and an electron-emitting spot carried by said boss.

12. In an electron beam tube of the fluorescent screen type for color television an indirectly heated cylindershaped cathode, the axis of which is arranged perpendicularly to the tube axis, several electron-emitting spots being arranged along the axis and carried by the cylindrical surface of said cathode, said cathode being surrounded by several separate concentric cylindrical control electrodes arranged along its axis, said control electrodes being provided with apertures arranged in the direction of the electron beam radially emitted from said spots.

References Cited in the file of this patent UNITED STATES PATENTS 1,797,990 Lucian Mar. 24, 1931 2,477,594 Glauber Aug. 2, 1949 2,506,627 Barford May 9, 1950 

